Liquid chromatography, which provides the ability to separate a fluid sample, for instance to purify or concentrate an analyte in a fluid sample, has proven to be of great assistance in a variety of analytical applications. For instance, the ability to assay the contents of test samples has proven extremely useful in the testing and examination of biological samples, in particular as analytical testing of biological samples often calls for a wide variety of tests and examinations from a starting sample of a very small volume. Polymeric stationary/support phases have been under investigation for over fifty years for use in liquid chromatography, e.g., high performance liquid chromatography (HPLC). Polymeric phases have been evaluated and implemented for the separation of ions, small molecules, and macromolecules. Common implementations of polymeric stationary phases can take a fibrous form including hollow or cylindrical solid fibers, rolled fabric, fiber staples, and continuous fiber phases, as well as the more common polymer beads/particulates and monoliths. These polymeric solid phases (used generically here to refer to polymeric stationary/support phases) generally offer common benefits over more widely applied porous silica-based stationary phases including chemical robustness and ease of chemical derivatization. Additional beneficial features of a polymeric fiber format include improved mass transfer due to the nonporous nature of the solid and convective diffusion throughout the column structure.
One specific type of fiber that has been described for use in liquid chromatography is the capillary-channeled polymer fiber (see, e.g., U.S. Pat. No. 7,740,763 to Marcus, et al.; U.S. Pat. No. 7,374,673 to Marcus, and U.S. Pat. No. 7,261,813 to Marcus, et al., all of which are incorporated herein by reference). Capillary-channeled polymer fibers have a unique shape as illustrated (as one example) in FIG. 1 that includes multiple channels that extend along the axial length of the fiber. The channels promote a self-alignment of the fibers when packed, for instance into an HPLC column, with interdigitation of the fibers (FIG. 2) resulting in a distribution of micron-sized open channels that run the length of the column. Capillary-channeled fibers can have two to three times more surface area in comparison to circular cross section polymer fibers of the same nominal diameter. The capillary channels of a column packed with the fibers are very efficient at fluid transport, allowing for traditional column sizes to be operated at high linear velocities while maintaining low back pressures. As a result, a column including capillary-channeled fibers can provide for high throughput and high efficiency separation, for instance separation of biomacromolecules.
While polymeric solid phase materials such as capillary-channeled fibers have provided great improvement to separation technologies, there remains a desire to perform more highly selective separations and extractions. Recent research has focused on the ability to modify the surface of the polymeric solid phase, allowing for more specific analyte-surface interactions. Modification has been approached to date through active end group generation methods including aminolysis, hydrolysis, and exposure to strong bases (i.e. NaOH or permanganate). These straightforward approaches produce a high, in some cases too high, density of functional groups such as —COOH, —NH, —OH, —CONH, etc. on the fiber surface for either analyte interaction or further modification processing under mild ambient conditions. Unfortunately, these approaches to polymeric solid phase modification are detrimental to the physical structure of the solid material as they can break down the basic polymer/fiber backbone. The well-established approach of plasma grafting to polymer surfaces has also been evaluated as a means to generate tailored surfaces without compromise of phase integrity. For example, a grafting-to approach has been evaluated utilizing polyacrylic acid (PAA) as a means of generating an anionic surface on a polymeric fiber to immobilize transition metal ions from aqueous solution. Unfortunately, the polymeric fiber and column structure provided a challenge in the grafting process, resulting in a non-uniform oxidation and therefore heterogeneous distributions of active sites.
What is needed in the art are improved sorbent media for separation applications that can address these and other problems in the art. For example, what is needed in the art is a more generalized approach to surface modification of a polymeric solid phase while still imparting specificity for the desired solid phase separation technology.